ADF (Auto Document Feeder) devices permitting mixing of documents with different sizes are widespread. Furthermore, ADF devices loaded with a document tray vertically movable are widespread as well. This is because the number of documents that can be placed on document tray is increasing.
Such ADF devices enable the document tray to move to a position of a document feed roller after a predetermined time has elapsed since a document on the document tray is detected, thereby reducing a waiting time of a user.
However, it is difficult for the user to correctly set the documents with different sizes on the document tray within the above-mentioned predetermined time. Furthermore, even if the user places the documents with different sizes on the document tray at once while aligning them, there is a possibility that the documents shift on the document tray and become skewed.